In situ conversion of heavy hydrocarbons to catalytic gas

ABSTRACT

A method of producing natural gas from a heavy hydrocarbon-containing subterranean formation includes: placing a catalyst having at least one transition metal into the formation, injecting an anoxic stimulation gas into the formation, and collecting the natural gas generated in the formation. The method may be performed outside the context of a subterranean formation under controlled conditions. Thus, a method of producing natural gas from bitumen includes: providing an anoxic mixture of heavy hydrocarbons and a catalyst having at least one transition metal, adding an anoxic stimulation gas to the mixture, and heating the mixture in the presence of the stimulation gas.

This application is a continuation-in-part of PCT applicationPCT/US07/60215 filed Jan. 8, 2007 which in turn claims the benefit ofU.S. Provisional Patent Application No. 60/757,168 filed Jan. 6, 2006and is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates in general to the production of naturalgas from high molecular weight hydrocarbons.

BACKGROUND

Heavy hydrocarbons such as bitumen, kerogen, Gilsonite®, and tars arehigh molecular weight hydrocarbons frequently encountered insubterranean formations. These hydrocarbons range from thick viscousliquids to solids at ambient temperatures and are generally quiteexpensive to recover in useful form. Bitumen occurs naturally in tarsands in locations such as Alberta, Canada and in the Orinoco oil beltnorth of the Orinoco river in Venezuela. Kerogens are the precursors tofossil fuels, and are also the material that forms oil shales. Kerogens,believed to be the precursor to bitumens, are frequently found insedimentary rock formations.

Heavy hydrocarbons in general, have been used in a number ofapplications such as in asphalt and tar compositions for paving roadsand roofing applications and as an ingredient in waterproofingformulations. Importantly, they are a potentially valuable feedstock forgenerating lighter hydrocarbons. This is typically accomplished bythermal cracking and hydrogenolysis processes, for example.

Recovering heavy hydrocarbons whole or as lighter hydrocarbons and/ornatural gas by thermal cracking in subterranean formations continues tobe a challenge. The excessive temperatures necessary for thermal (orsteam) cracking (about 850° C.) requires expensive, complex technologydue to the special construction material to sustain high crackingtemperatures and high energy input. Hydrogenolysis has limited utilitywhen the recovery of lighter hydrocarbons is desirable. This is due tothe difficulty of separating hydrogen from light olefins such asethylene, propylene, and natural gas. Therefore, there is a continuingneed for the development of methods for producing light hydrocarbons andnatural gas from high molecular weight hydrocarbon feedstocks.

SUMMARY OF THE INVENTION

In view of the foregoing and other considerations, the present inventionrelates to a method for the catalytic conversion of heavy hydrocarbonsto natural gas.

Accordingly, a method of producing natural gas from a heavyhydrocarbon-containing subterranean formation includes: placing acatalyst comprising at least one transition metal into the formation,injecting a stimulation gas containing less than 1 ppm oxygen (hereafterreferred to as ‘anoxic’) into the formation, and collecting the naturalgas generated in the formation.

A method of producing natural gas from heavy hydrocarbons includes:providing a mixture of heavy hydrocarbons and a catalyst that includesat least one transition metal, adding an anoxic stimulation gas to themixture, and heating the mixture in the presence of the stimulation gas.

A method of forming natural gas includes: providing a mixture of heavyhydrocarbons and a catalyst having at least one transition metal; addingan anoxic stimulation gas to the mixture, and heating the mixture in thepresence of the stimulation gas

The foregoing has outlined the features and technical advantages of thepresent invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of the invention will be described hereinafter which form thesubject of the claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and aspects of the present inventionwill be best understood with reference to the following detaileddescription of a specific embodiment of the invention, when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is a plot showing the generation of methane and ethane over timefrom Barnett Shale in flowing helium at 250° C.

FIG. 2 is a plot showing the generation of methane and ethane over timefrom Monterey source rock KG-4 in flowing helium at 250° C.

FIG. 3 a is a plot showing gas chromatographic analyses of the amountand types of gasses produced from a sample of New Albany shale subjectto an isothermal helium flow, at 100° C. and 350° C. under anoxic heliumflow.

FIG. 3 b is a plot showing gas chromatographic analyses of the amountand types of gasses produced from a sample of New Albany shale subjectto a flow of helium with 10 ppm O₂ at 100° C. and 350° C.

FIG. 4 is a plot showing gaseous hydrocarbon evolution over 21.7 hoursat 50° C. from a sample of shale from Black Warrior Basin.

DETAILED DESCRIPTION

Embodiments disclosed herein are directed to a method in which varioustransition metal-containing catalysts present as zero- or low-valentmetal complexes, are co-injected with sand or other proppant intoreservoirs rocks under sufficiently high pressures to fracture the rocksthus creating conduits of porous sand through which the transition metalcomplexes can pass into the regions of the formation containing heavyhydrocarbon materials. Alternatively, the catalysts may be delivered tohydrocarbon-containing sites within a formation using muds.

The method further includes closing the well (after introduction ofstimulation gases) for sufficient time to allow metal catalyzeddecomposition of bitumen (digestion) and gas generation. Thus, a methodof producing natural gas from a heavy hydrocarbon-containingsubterranean formation includes placing a catalyst which has at leastone transition metal into the formation, injecting an anoxic stimulationgas into the formation (in some embodiments simultaneous with catalystintroduction), and collecting the natural gas generated in theformation.

Heavy Hydrocarbons: Heavy hydrocarbons as used herein include, but isnot limited to all forms of carbonaceous deposits with sufficienthydrogen to convert to natural gas: (—CHx—)→gas+(—CHy—) where x>y.Examples include kerogens, solid hydrocarbons (Gilsonite, tars and thelike), and bitumens. Such heavy hydrocarbons may be processed in situ ina formation. Alternatively, any of the hydrocarbons may also be reactedoutside the context of a subterranean location, for example, in a batchreactor under carefully controlled conditions. Such conditions wouldinclude, for example, the substantial removal of oxygen which is proneto poisoning transition metal catalysts.

Catalyst: Typical source rocks, usually shales or limestones, containabout 1% organic matter, although a rich source rock might have as muchas 20%. Source rocks convert their bitumen to natural gas at moderatetemperatures (25 to 200° C.) in their natural state without hydrogenaddition (see Experimental examples below). They do so chaotically, withrandom bursts of activity within periods of little or no activity, aphenomenon not uncommon in transition metal catalysis. Such behavior hasbeen observed in a number of hydrogenation reactions including thehydrogenation of carbon monoxide, ethylene, and nitric oxide over Ni,Pt, Pd, Ir, Rh, and Ag (Eiswirth, M., 1993. Chaos in surface-catalyzedreactions. Ch. 6 in Chaos in Chemistry & Biochemistry, eds. R. J. Field& L. Gyorgyi, World Scientific Publishing Co., River Edge, N.J., USA,141-174.) and in the hydrogenolysis of ethane over Ni and Pd (Kristyan,S., and Szamosi, J., 1992. Reaction kinetic surfaces and isosurfaces ofthe catalytic hydrogenolysis of ethane and its self-poisoning over Niand Pd catalysts. Computers in Physics 6, 494-497.). Indeed, suchchaotic behavior is an identifying characteristic of transition metalcatalysis.

Therefore, in some embodiments, the method of converting heavyhydrocarbons to natural gas (oil-to-gas) may be accelerated in situ byinjecting transition metals into reservoir rocks. The catalystcomponents may be obtained from an active source rock by isolation ofthe transition metals from active source rock. Alternatively, the sourcerock itself may be used without isolation of the individual activetransition metals by generating a fine powder form of the source rock.One skilled in the art will recognize that under heterogeneousconditions high catalytic activity may be achieved by having catalystparticles with large surface area to volume ratios. Thus, it may beparticularly beneficial to mill the source rock to very small particlesize, for example, 10 nm-10,000 nm average diameter, though largerparticles may be used as well.

In yet other embodiments, purified reagent grade transition metalcomponents may be used and mixed in appropriate concentrations toreflect the naturally occurring compositions. For example, active sourcerocks may contain sufficient low-valent transition metals (100 to 10,000ppb) to promote the reaction at reservoir temperatures (100° C. to 200+°C.) on a production time scale (days to years). Source rock activitiesmay be determined experimentally in flowing helium at varioustemperatures. An assay procedure has been described by Mango (U.S. Pat.No. 7,153,688).

The transition metal may be a zero-valent transition metal, a low-valenttransition metal, alloys, and mixtures thereof. Any transition metalthat serves as a hydrogenation catalyst may be viable as a catalyst forthe disproportionation reaction of heavy hydrocarbons. Varioustransition metals catalyze the hydrogenolysis of hydrocarbons to gas(Somorjai, G. A., 1994. Introduction to Surface Chemistry and Catalysis.John Wiley & Sons, New York. pg. 526); for example, C₂H₆+H₂→2 CH₄. Ithas also been demonstrated that source rocks are catalytic in thehydrogenolysis of hydrocarbons (Mango, F. D. (1996) Transition metalcatalysis in the generation of natural gas. Org. Geochem. 24, 977-984.)and that low-valent transition metals are catalytic in thehydrogenolysis of crude oil (Mango, F. D., Hightower, J. W., and James,A. T. (1994) Role of transition-metal catalysis in the formation ofnatural gas. Nature, 368, 536-538.). Furthermore, there is substantialevidence that low-valent transition metals are active agents insedimentary rocks (U.S. patent application Ser. No. 11/006,159). Activesource rock may include transition metals such as molybdenum, nickel,cobalt, iron, copper, palladium, platinum, rhodium, ruthenium, tungsten,rhenium, osmium, and iridium.

The catalyst components may be immobilized and introduced into theformation on a proppant, in some embodiments. Alternatively, catalystsmay be injected as gases, metal carbonyls, for example, which coulddissolve in the carbonaceous sediments, decompose with time, thusdelivering to the sediments low-valent active metals such as Ni, Co, Fe.Alternatively, the catalyst may be introduced at various stages inoil-based muds, for example. Fine metal particles could also be injecteddirectly with sand in reservoir fracturing, thus dispersing fineparticles of active catalyst throughout the network of porous sandconduits that carry hydrocarbons from the reservoir to the surface.Catalysts may be coated with paraffins (C₈ to C₁₈) to protect them fromoxygen-poisoning while on the surface and during injection into thereservoir.

Stimulation gas: Since active metals in natural sedimentary rocks arepoisoned irreversibly by oxygen (U.S. Pat. No. 7,153,688), it isbeneficial that the stimulation be anoxic (<1 ppm O₂). Trace amounts ofoxygen picked up in processing can be easily and inexpensively removedwith commercial oxygen scrubbers. The stimulation gas may includenatural gas, gas depleted of methane, carbon dioxide, helium, argon, andnitrogen. For natural gas (catalytic gas) production, hydrogen gas mayinterfere with separation and therefore is not an ideal stimulation gas.Again, the stimulation gas may also be used not only for the fracturing,but also as a means of depositing the catalyst within the formation. Insome embodiments, the stimulation of catalytic gas generation frombitumen in reservoir rocks may be achieved through a single well bore ina permeable reservoirs by injecting and withdrawing gas sequentially tocreate sufficient turbulence to stimulate chaotic gas generation or itmay be achieved through multiple injection wells positioned to maximizecontinuous gas flow through the permeable reservoir to production wellsthat collect the injected gas plus catalytic gas. Production units wouldcollect produced gas, injecting a fraction to maintain a continuousprocess and sending the remainder to market.

In reservoirs with insufficient permeability to sustain gas flow such astight shales like the Mississippian Barnett Shale in the Fort WorthBasin (TX), fracturing the reservoir may be beneficial. Fracturing maybe accomplished with injected sand or other appropriate proppant tocreate interlacing conduits of porous sand to carry injected gas throughthe reservoir to conduits of porous sands that carry the injected gasplus catalytic gas from the reservoir to production units. The flowinggas injected into the reservoir stimulates catalytic activity within theshale.

Fracturing may also be used to expose active catalytic sites inherent inshales and other heavy hydrocarbon-containing formations. Care should betaken in the fracturing process to minimize the exposure of thesefreshly exposed catalytic sites to oxygen and other oxidants that maydeactivate low valent transition metal catalysts. Elemental oxygen inexcess of 1 ppm can reduce the effectiveness of the catalytic reactionwith heavy hydrocarbons. It has been observed, however, that thispoisoning of catalytic activity is temperature sensitive. Attemperatures lower than about 50° C. catalytic activity may beunaffected by the presence of oxygen, for example. For the commonfracturing fluid water, a simple degassing procedure prior to fracturingmay be sufficient to protect the nascent catalytic sites exposed duringfracturing. In order to establish natural gas production afterfracturing, the stimulation gas is simply allowed to flow over the newlyfractured formation.

Injected gas may be natural gas produced from the deposit or natural gasproduced from another deposit elsewhere. The process could be carriedout by sequential injections where the reservoir is pressured, thenallowed to stand and exhaust its induced pressure over time. Thisprocess could be repeated multiple times until the reservoir wasexhausted of heavy hydrocarbons. The process could also be carried outin a continuous mode where gas is injected continuously into one welland withdrawn continuously from another. The two wells (or multiplewells) would be interconnected through a production unit that withdrawsproduced gas from the system sending excess gas to market andre-injecting the remainder to sustain continuous production.

Heavy hydrocarbon to natural gas: In addition to methods for in situcracking of heavy hydrocarbons in a subterranean location, one may alsoproduce natural gas from isolated heavy hydrocarbons in batch reactors,for example. To carry out such production the method entails mixingisolated heavy hydrocarbons (for example mined bitumen) with an activecatalyst as described above. An anoxic stimulation gas may be introducedand the mixture heated under anoxic conditions.

Again the catalyst may be an active source rock ground into fine powderas described above. Alternatively, the active transition metalcomponents may be isolated from the source rock or stock mixturesprepared from commercially available sources in proportions identifiedin high activity source rock.

The stimulation gas may be natural gas, natural gas depleted of methane,carbon dioxide, helium, argon, and nitrogen. In the context of batchreaction, such a stimulation gas may be provided as a flow while heatingthe bitumen catalyst mixture. Catalytic activity may be facilitated byheating in a range from about 25° C. to about 350° C. and from about 25°C. to about 250° C. in other embodiments. In particular embodiments,heating may be carried out in a range from about 100° C. to about 200°C. In all embodiments, it is beneficial that the stimulation gas beanoxic (<1 pp O₂).

Methods disclosed herein may be used in the production of natural gas(catalytic gas). The aforementioned method for the disproportionation ofbitumen and high molecular weight hydrocarbons may be used in suchproduction. This may be carried out in batch reactors, or generateddirectly from tar sand sources where it may be collected in the fieldand distributed commercially.

The following example is included to demonstrate particular embodimentsof the present invention. It should be appreciated by those of skill inthe art that the methods disclosed in the example that follows merelyrepresent exemplary embodiments of the present invention. However, thoseof skill in the art should, in light of the present disclosure,appreciate that many changes can be made in the specific embodimentsdescribed and still obtain a like or similar result without departingfrom the spirit and scope of the present invention.

EXAMPLE 1 Barnett Shale, 250° C., Helium

In a typical anoxic procedure, rocks are ground to powders (60 mesh)under pure argon to protect their inner surfaces from oxidation. Thesepowders are then transferred to 5 ml ½ inch tubular brass reactors (newreactors were constructed for most experiments) that are secured at eachend to ¼ inch copper tubing through Swagelok fittings. The tubing isattached to gas lines through valves to open and close the system to gasflow. Reactors (pressure-tight) are flushed with flowing gas (helium, 12cc/min) for 10 minutes at room temperature to remove any air picked upin reactor assembly. They are pressure flushed (purified helium) fivetimes by pressuring to 50 psi and venting to one atmosphere to removeany remaining oxygen and residual light hydrocarbons (adsorbed in theshales) that might interfere with the analysis. Reactors (now anoxic)are then heated (12.5° C./min) under purified helium flow to reactiontemperatures where gas flow is continued at constant temperatures.

In this example, a sample of Barnett shale (Mississippian, Ft. WorthBasin Tex.) (3.4 g), ground to a powder in anoxic argon, was placed in areactor and purged of any adsorbed oxygen by flowing anoxic helium(through a commercial oxygen scrubber) through the reactor at 350° C.for 20 minutes. Helium flow (12 mL/min) was continued at 250° C. forover one hour while the effluent (i.e. stimulation) gas was monitoredfor methane by a FID as shown in FIG. 1. The first methane peak(presumably adsorbed and catalytic methane from the 10 min purge at 350°C.) emerged at 12.5 min (5.8×10⁻⁵ g CH₄) followed by a flat baselineover the next 20 min showing that the sample was no longer releasingmethane. Three sharp peaks of increasing intensity then appeared at 45min. (9.9×10⁻⁶ g CH₄), 68 min. (1.6×10⁻⁵ g CH₄), and 94 min. (5.6×10⁻⁵ gCH₄). The final three peaks constitute 2.2×10⁻² mg CH₄/(g rock hr) whichis greater than that for this rock under our usual conditions (inhydrogen) (5.7×10⁻³ mg CH₄/(g rock hr).

EXAMPLE 2 Monterey Source Rock, 250° C., Helium

A sample of Monterey shale (Miocene, Calif.) (KG-4) (1.64 g) wasanalyzed under identical conditions under pure helium flow for about 7hours (FIG. 2). After the initial peak of adsorbed gas (3 min., 2.7×10⁻⁶g CH₄), three very large peaks emerged after 5 hours of He flow, thefirst corresponding to 7.3×10⁻⁴ g CH₄, the second (180 min. later) to2.2×10⁻⁴ g CH₄, and the third (285 min. after the first) to 1.1×10⁻⁴ gCH₄, with an overall rate of 0.2 mg CH₄/(g rock hr), not materiallydifferent from that under hydrogen.

EXAMPLE 3 Barnett Shale, 200° C., Helium

Pure helium (passed through an oxygen scrubber) was passed over a sampleof Barnett Shale (2.88 g) (ground to a powder (60 mesh) in argon) at200° C. for 140 minutes producing a burst of methane (4×10⁻² mg)corresponding to a rate of 8.3×10⁻³ mg CH₄/(g rock hr), a ratesubstantially greater than that obtained from the same experiment inhydrogen (3.6×10⁻⁵ mg CH₄/(g rock hr)) at this temperature and onlyslightly lower than that at 250° C.

It was observed that activity increases only slightly with temperaturein helium suggesting rate suppression counteracting the usual Arrheniusexponential rate increase with temperature. The higher-than-expectedactivities observed in helium at 200° C. suggests higher thananticipated activities at subsurface temperatures and the expectation ofpromoting the conversion of heavy hydrocarbon to natural gas at moderatereservoir temperatures by injecting low-valent active transition metalsinto these reservoirs.

EXAMPLE 4

A Monterey shale (Miocene, Calif.) sample generates methane at a rate of˜6×10⁻⁶ g C₁/(g rock hr) in hydrogen gas containing 3% propane underclosed conditions (30 minutes) at 250° C. and generates very littlemethane at 200° C. under the same conditions (30 minutes). Under flowinghelium at 200° C., the same rock converts its bitumen to gas at a rateof 1.3×10⁻⁴ g C₁/(g rock hr). These results suggest that themass-transfer stimulation gas may achieve two positive effects: 1) ittransports hydrocarbons from heavy hydrocarbon deposits to activecatalytic sites, and 2) it removes activity-suppressing agents(products' and adsorbents) from the active sites catalyst surfaces.

EXAMPLE 5

Marine shales generate two distinct gases in the laboratory, one at hightemperatures (>300° C.) from kerogen cracking, and the other at lowtemperatures (<100° C.) through the catalytic action of low-valenttransition metals as shown in exemplary FIGS. 3 a and 3 b. The data inFIGS. 3 a and 3 b were obtained from a sample of New Albany shalesubject to an isothermal helium flow, at 100° C. and 350° C.,sequentially. FIG. 3 a shows the system under an anoxic helium flow.FIG. 3 b shows the system with a flow of helium with 10 ppm O₂. NewAlbany shale generates catalytic gas dominated by propane. Thus, thehigh-propane peaks at 100 and 350° C. are catalytic gas peaks. Thermalgas from kerogen cracking is represented by the methane peak (500 ppmvol) at 350° C. Catalytic gas is 90% of the total gas in FIG. 3 a.

Low-temperature gas generation is unique. Generation rates are orders ofmagnitude higher, product compositions are dynamic, kinetics ofgeneration are non-linear, and gas generation terminates on exposure totrace levels of oxygen. Equally surprising, different shales generategases having different compositions. Barnett Shale, Fort Worth basin,generates a gas enriched in methane and near thermodynamic equilibriumin C₁-C₃ (K=[(C₁)(C₃)]/[C₂)²]), while New Albany Shale, Illinois basin,generates a gas with mainly propane, and not at equilibrium, although itapproaches equilibrium over time.

EXAMPLE 6

Cuttings of marine shale from the Black Warrior Basin were ground topowders (60 mesh) in argon (1.31 g) and placed in a metal reactor andprepared for reaction as described before (pressure-purging the reactorwith pure helium, etc). The reactor was then warmed to 50° C. underanoxic helium flow and the products in the effluent stream were analyzedby FID. The product gas stream was passed directly into the FIDbypassing all cold traps. The trace represents the FID signal over time(minutes). Since the product stream bypassed all cold traps, the fourpeaks represent all gaseous hydrocarbons generated from the shale. Thisproduced four distinct signals of gas production at 308.8, 516.7, 728.6,and 927.9 minutes, as shown in FIG. 4, corresponding to 70 μg gas/gshale. This experiment provides the clearest example of chaotic kineticsand thus additional evidence of catalytic action by transition metals(Field & Gyorgyi, Chaos in Chemistry & Biochemistry, World ScientificPub. Co, River Edge, N.J., 1993; Eiswirth, Ch 6 in Chaos in Chemistry &Biochemistry, 1993).

Low-temperature gas forms at temperatures comparable to geologicalreservoir temperatures, but only when there is gas flow under anoxicconditions. This is achieved in the laboratory by grinding the shales inpure argon to expose inner anoxic surfaces, and then passing purifiedhelium over the surfaces at constant temperature. In a typical example,a Paleozoic marine shale (Chattanooga/Floyd) from the Black WarriorBasin (Alabama/Mississippi) generated 70 μg gas/(g shale) in 21.7 hoursat 50° C.

Two things are remarkable about these results. First, is the robustactivity at a very low temperature. Rates of most chemical reactionsdiminish with decreasing temperatures. Higher reaction temperatures maybe suppressing activity or otherwise altering the chaotic kinetics ofcatalytic gas generation. Without being bound by mechanism, anoxic gasflow stimulates gas generation at very low temperatures, in this exampleat 50° C., and thus, gas-flow stimulated gas generation may be viable atall subsurface temperatures. Generating gas without injecting heat maybe viable because of the thermodynamic stability of light hydrocarbonsover the heavier hydrocarbons. The conversion of pentane to methane,propane, and carbon at 27° C., for example, is exothermic by −15.81kcal/mole (Stull et Al., The Chemical Thermodynamics of OrganicCompounds, John Wiley & Sons, N.Y., 1969). Thus the conversion ofbitumen to gas is energetically favorable at most reservoir temperaturesand requires no heat input to drive conversion. The second remarkablething is the duration of sustained high activity, in this case over 22hours. This means that a shale like this one in the subsurface at thistemperature would generate about 4 MMcft/(acre-ft year) under gas-flowstimulation.

Advantageously, the methods describe herein provide a means for recoveryuseful catalytic gas from heavy hydrocarbons in situ from subterraneanformations. When used in situ at the site of a formation, the conversionof heavy hydrocarbon extends the useful lifetime of reservoir enhancingthe oil recovery process. The same process may be duplicated undercontrolled conditions in batch reactors for commercial production ofnatural gas. Furthermore, the availability of certain heavyhydrocarbons, such as bitumen, from renewable resources may provide anenvironmentally sound means for natural gas production.

All patents and publications referenced herein are hereby incorporatedby reference to the extent not inconsistent herewith. It will beunderstood that certain of the above-described structures, functions,and operations of the above-described embodiments are not necessary topractice the present invention and are included in the descriptionsimply for completeness of an exemplary embodiment or embodiments. Inaddition, it will be understood that specific structures, functions, andoperations set forth in the above-described referenced patents andpublications can be practiced in conjunction with the present invention,but they are not essential to its practice. It is therefore to beunderstood that the invention may be practiced otherwise than asspecifically described without actually departing from the spirit andscope of the present invention as defined by the appended claim.

From the foregoing detailed description of specific embodiments of theinvention, it should be apparent that a novel method for convertingbitumen to natural gas has been disclosed. Although specific embodimentsof the invention have been disclosed herein in some detail, this hasbeen done solely for the purposes of describing various features andaspects of the invention, and is not intended to be limiting withrespect to the scope of the invention. It is contemplated that varioussubstitutions, alterations, and/or modifications, including but notlimited to those implementation variations which may have been suggestedherein, may be made to the disclosed embodiments without departing fromthe spirit and scope of the invention as defined by the appended claimswhich follow.

1. A method of producing natural gas from a heavy hydrocarbon-containingsubterranean formation comprising: placing a catalyst comprising atleast one transition metal into the formation; injecting an anoxicstimulation gas into the formation, wherein said stimulation gas is nothydrogen; and collecting the natural gas generated in the formation. 2.The method of claim 1, wherein the catalyst is provided from an activesource rock.
 3. The method of claim 1, wherein the catalyst is providedon a proppant.
 4. The method of claim 1, wherein at least one transitionmetal is selected from the group consisting of a zero-valent transitionmetal, a low-valent transition metal, alloys, and mixtures thereof. 5.The method of claim 4, wherein the at least one transition metal isselected from the group consisting of molybdenum, nickel, cobalt, iron,copper, palladium, platinum, rhodium, ruthenium, tungsten, osmium,rhenium, and iridium.
 6. The method of claim 1, wherein the stimulationgas is at least one selected from the group consisting of natural gas,natural gas depleted of methane, carbon dioxide, helium, argon, andnitrogen.
 7. A method of producing natural gas from heavy hydrocarbonscomprising: providing a mixture comprising: heavy hydrocarbons; and acatalyst comprising at least one transition metal; adding an anoxicstimulation gas to the mixture; wherein the stimulation gas is nothydrogen; and heating the mixture in the presence of the stimulationgas.
 8. The method of claim 7, wherein the catalyst is provided from anactive source rock.
 9. The method of claim 7, wherein the at least onetransition metal is selected from the group consisting of a zero-valenttransition metal, a low-valent transition metal, alloys, and mixturesthereof.
 10. The method of claim 9, wherein the at least one transitionmetal is selected from the group consisting of molybdenum, nickel,cobalt, iron, copper, palladium, platinum, rhodium, ruthenium, tungsten,osmium, rhenium, and iridium.
 11. The method of claim 7, wherein thecatalyst further comprises salts of at least one main group elementselected from the group consisting of sulfur, phosphorus, arsenic, andantimony.
 12. The method of claim 7, wherein the anoxic stimulation gasis at least one selected from the group consisting of natural gas,natural gas depleted of methane, carbon dioxide, helium, argon, andnitrogen.
 13. The method of claim 7, wherein heating is carried out in arange from about 25° C. to about 250° C.
 14. The method of claim 13,wherein heating is carried out in a range from about 100° C. to about200° C.
 15. A method of forming natural gas comprising: providing ananoxic mixture comprising: heavy hydrocarbons; and a catalyst comprisingat least one transition metal; adding an anoxic stimulation gas to themixture; wherein the stimulation gas is not hydrogen; and heating themixture in the presence of said stimulation gas.
 16. The method of claim15, wherein the catalyst is provided from an active source rock.
 17. Themethod of claim 15, wherein the at least one transition metal isselected from the group consisting of a zero-valent transition metal, alow-valent transition metal, alloys, and mixtures thereof.
 18. Themethod of claim 17, wherein the at least one transition metal isselected from the group consisting of molybdenum, nickel, cobalt, iron,copper, palladium, platinum, rhodium, ruthenium, tungsten, osmium, andiridium.
 19. The method of claim 15, wherein the anoxic stimulation gasis at least one selected from the group consisting of natural gas,natural gas depleted of methane, carbon dioxide, helium, argon, andnitrogen.
 20. The method of claim 15, wherein heating is carried out ina range from about 25° C. to about 350° C.
 21. A method of stimulatingnatural gas production in a heavy hydrocarbon-containing subterraneanformation comprising: fracturing the formation in a substantiallyoxidant free environment; and adding an anoxic stimulation gas to thefractured formation.
 22. The method of claim 21 further comprisingwithdrawing gases generated by the addition of the anoxic stimulationgas.